TRV in Buffalo and medical exam

Hi,
My temporary resident visa (TRV) is expiring in March. I was planning on going to Buffalo to renew it (as I live in Toronto).
I understand that if you apply in person its 'same day' to process the application if it is straight forward, however, what happens if you need a medical exam? I am a registered nurse in Toronto so I am 100% certain that I will need a medical exam.

- Will they give me my passport back in order to come back to Toronto to do the medical exam? I have heard that they do give your passport back and give you the paperwork to do the medical exam AND if everything is to their satisfaction, they will ask you to mail your passport so they can issue the visa.

Please advise if you have any knowledge on this matter.

Thanks
NB